Climate scientists have concluded that temperatures could jump by up to 9F
(5C) and sea levels could rise by up to 2ft 8ins (82cm) by the end of the
century, according to a leaked draft of a United Nations report.

The UN Intergovernmental Panel on Climate Change also said there was a 95 per cent likelihood that global warming is caused by human activities. That was the highest assessment so far from the IPCC, which put the figure at 90 per cent in a previous report in 2007, 66 per cent in 2001, and just over 50 per cent in 1995.

Reto Knutti, a professor at the Swiss Federal Institute of Technology in Zurich, said: “We have got quite a bit more certain that climate change is largely man-made. We’re less certain than many would hope about the local impacts.”

The IPCC report, the first of three in 2013 and 2014, will face intense scrutiny particularly after errors in the 2007 study, which wrongly predicted that all Himalayan glaciers could melt by 2035.

Almost 200 governments have agreed to try to limit global warming to below 3.6F (2C) above pre-industrial times, which is seen as a threshold for dangerous changes including more droughts, extinctions, floods and rising seas that could swamp coastal regions and island nations. Temperatures have already risen by 1.4F (0.8C) since the Industrial Revolution.

The report will say there is a high risk global temperatures will rise by more than 3.6F this century. They could rise anywhere from about 1F to almost 9F, a wider range at both ends of the scale than predicted in the 2007 report.

It will also say evidence of rising sea levels is “unequivocal”. The report projects seas will rise by between 1ft and 2ft 8ins by the late 21st century. In 2007 the estimated rise was between 7ins and 23ins, but that did not fully account for changes in Antarctica and Greenland.

Scientists say it is harder to predict local impacts. Drew Shindell, a Nasa scientist, said: “I talk to people in regional power planning. They ask, 'What’s the temperature going to be in this region in the next 20 to 30 years, because that’s where our power grid is?’ We can’t really tell.”

The IPCC will try to explain why global temperatures, have risen more slowly since about 1998 even though greenhouse gas concentrations have hit record highs in that time. It could be due to a combination of ash from volcanoes dimming sunlight, a decline in heat from the sun during the solar cycle, and the possibility that the climate may be less sensitive than expected to carbon dioxide build-up.